Abstract

Bats that glean prey (capture them from surfaces) produce relatively inconspicuous echolocation calls compared to aerially foraging bats and could therefore be difficult predators to detect, even for insects with ultrasound sensitive ears. In the cricket Teleogryllus oceanicus, an auditory interneuron (AN2) responsive to ultrasound is known to elicit turning behaviour, but only when the cricket is in flight. Turning would not save a cricket from a gleaning bat so we tested the hypothesis that AN2 elicits more appropriate antipredator behaviours when crickets are on the ground. The echolocation calls of Nyctophilus geoffroyi, a sympatric gleaning bat, were broadcast to singing male and walking female T. oceanicus. Males did not cease singing and females did not pause walking more than usual in response to the bat calls up to intensities of 82 dB peSPL. Extracellular recordings from the cervical connective revealed that the echolocation calls elicited AN2 action potentials at high firing rates, indicating that the crickets could hear these stimuli. AN2 appears to elicit antipredator behaviour only in flight, and we discuss possible reasons for this context-dependent function.

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Acknowledgments

Thanks to Reese Arh for data analysis and Peter Wall for the custom MATLAB sound-generating and spike analysis applications. The manuscript was greatly improved by comments from Holger Görlitz, Fernando Montealegre-Zappata, and two anonymous reviewers. Funding was provided by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grant to JHF, University of Toronto undergraduate research support to JK, and an NSERC postgraduate scholarship to HMtH.